The present invention relates generally to the removal of phosphorus from waste waters and more particularly to methods and materials, involving the microorganism Acinetobacter phosphadevorus (NRRL B-8058), providing effective removal of phosphorus in sewage within the framework of available activated sludge treatment systems.
The presence of large amounts of phosphorus-containing compounds, particularly orthophosphates, in sewage and other waste waters is believed to be partially responsible for eutrophication, through uncontrolled growth of algae, of lakes and waterways throughout the world. [See, e.g., Hammond, A. E., Science 172, pp. 361-3 (1971).] Control of phosphorus levels of below 0.5 milligrams of orthophosphate per liter is generally believed necessary for the control of algal growth and it has been proposed that algal growth would almost cease if levels were controlled to below 0.05 milligrams per liter. [See, e.g., Nesbitt, J. B., Jour. Water Poll. Control Fed., 41, No. 5, pp. 701-713 (1969).] Phosphorus is most frequently removed from waste waters through chemical treatment, activated sludge treatment, or through a combination of both.
Chemical treatment ordinarily involves ion exchange and/or precipitation of phosphorus with metal ions such as aluminum, iron, or calcium. A review of chemical treatment schemes may be found in Jenkins, D., et al., Water Research, 5, 369 (1971).
The sludge employed in activated sludge systems is a sticky, muddy, brown to black mass of biological components such as bacteria, protozoa, and algae, as well as non-biological components such as organic products and inorganic materials, which forms naturally when waste water is aerated in tanks. In most treatment plants, sludge effectively rids the waste water of carbon compounds and potentially infectious bacteria, but does a rather poor job in removing phosphorus pollutants. Many sludges which can provide organic removals of 90 to 95% will take up phosphate at a rate of less than 1 milligram per liter per hour.
Activated sludge treatment schemes asserted to provide enhanced capability for removal of phosphorus are quite varied. U.S. Pat. No. 3,654,146, which itself relates to an activated sludge method involving "starving" of sludge microorganisms, contains a rather complete review of many prior art methods, particularly those of U.S. Pat. Nos. 3,236,766, 3,385,785, 3,390,077 and 3,522,171. The proposed schemes, if they are effectively practiced, ordinarily substantially increase the overall cost of waste water treatment either because of special apparatus or special chemicals.
Within the last five to seven years it has been reported that sludges, termed "luxury" sludges, from plants located in five cities (San Antonio, Fort Worth, and Amarillo, Tex.; Baltimore, Md.; and Los Angeles, Calif.) in the United States had high affinities for phosphorus. (See, e.g., Withrow, J. L., Proc. 24th Ind. Waste Conf., pp. 1169-84, Purdue University, Lafayette, Ind. (1969).)
Prior to the present invention, the mechanism by which sludges removed amounts of phosphorus in excess of their apparent metabolic requirements was subject to controversy, as evidenced by conflicting proposals and reports. With respect to the sludge of the Rilling Road plant in San Antonio, Tex., it was concluded in Menar, A. B., et al., SERL Report, 68- 6, U. Cal. Berkley (1968) that the high phosphorus affinity shown by Rilling shown sludge not biological in nature. It was therein proposed that excess removal, above that required for cell synthesis, was controlled by pH and the presence of calcium ions (Ca.sup.2.sup.+) in the waste water. Under proper conditions of pH, a precipitate of calcium phosphate would form followed by an enmeshing of the precipitate into the activated sludge floc. Subsequent settling of the sludge would result in apparent disappearance of the phosphate from the supernatant fluid and incorporation into the floc.
While it was variously proposed and reported that the mechanism of enhanced uptake was principally biological in nature, there was little elucidation of such proposals. There existed only limited information in the art concerning the role played by the various microbial components of activated sludge in phosphate uptake. Srinath, et al., Water and Waste Treatment, 11, pp. 410-416 (1967) reported investigations of the removal of radioactive phosphorus (.sup.32 P) from sewage by activated sludge, mixed bacterial cultures isolated from sludge, Zoogloea, sp., and the protozoan Epistylis sp. It was therein concluded that removal of .sup.32 P from sewage was due largely to vorticellid protozoa such as Epistylis sp. in sludge. While it was demonstrated that bacteria were responsible for uptake of some amount of .sup.32 P, since the bacteria remained dispersed in the medium, it was concluded that bacterial efficiency in removal was poor. Whether protozoa played a primary role in phosphorus removal or simply served as a means for concentrating phosphorus taken up by bacteria was unresolved in the reference.
Ongoing research by certain of the inventors and their co-workers revealed rather conclusively a biological basis for the enhanced capacity of Rilling plant sludge for phosphorus uptake. In their 1971 report for the Environmental Protection Agency, Mechanisms of Biological Luxury Phosphate Uptake (Water Pollution Control Research Series, 17010 DDQ 11/71) and in a companion publication, Boughton, W. H., et al., Applied Microbiology, 22, pp. 571-77 (1971), studies of metabolic factors affecting enhanced phosphorus uptake by Rilling sludge were reported. The disclosure of these references concerning metabolic factors is expressly incorporated by reference in this disclosure. Briefly stated, these two references showed that the Rilling (San Antonio, Tex.) sludge has the capability of removing all of the phosphate normally found in Tucson, Ariz. sewage (about 30 mg./l.) in less than 3 hours. Removal was independent of externally supplied sources of energy or ions, since added orthophosphate and H.sub.3.sup.32 PO.sub.4 radioactivity were readily removed from tap water, glass-distilled water, and deionized water. The uptake had an optimum temperature range (24.degree. to 37.degree.C.) and an optimum pH range (7.7 to 9.7). It was inhibited by HgCl.sub.2, iodoacetic acid, p-chloromercuribenzoic acid, NaN.sub.3, and 2,4-dinitrophenol.sub.3. Uptake was inhibited by 1% NaCl but was not affected by 10- 3 M. ethylenediaminetetraacetic acid.
The above-identified E.P.A. report concluded, however, that at least two types of enzyme systems or microbial populations existed which participated in the phosphorus uptake. The extensive bacterial survey therein reported was inconclusive in pinpointing any particular members of the bacterial population of Rilling sludge as responsible for the activity under study. A filamentous form, Sphaerotilus natans, was noted as having the best phosphorus affinity of those bacteria isolated, but its affinity could account for only about one tenth of the total sludge activity. It was therefore concluded that S. natans might be the primary phosphorus removing entity in a synergistic combination with one or more other microbial entities.
Further studies by certain of the inventors and their co-workers in attempting to ascertain the mechanism by which Rilling sludge removes phosphorus from its medium are reported in Yall, I., et al., "Logical Removal of Phosphorus," appearing at pp. 231-241 in Eckenfelder, W. W., et al., (ed.) Applications of New Concepts of Physical-Chemical Wastewater Treatment, Sept. 18-22, 1972 (Pergamon Press, Elmsford, N.Y. 1972).
Finally, in the 1973 doctoral dissertation of one of the co-inventors (Roinestad, F. A., "Volutin Accumulation by Activated Sludge Microorganisms," The University of Arizona, available through Dissertation Abstracts Int'l., No. 74-12, 437), there is reported the detection of a bacterium, designated "P-7", as one of seven elements within grape-like clusters of coccoid, gram-negative microorganisms in Rilling sludge. "P-7" was therein demonstrated, by staining studies, to have the capacity to form volutin (a granular complex of polyphosphate, RNA, proteins and lipids) in 21 kinds of common phosphate-containing media. The disclosure of the Roinestad dissertation is expressly incorporated by reference herein.